Aqueous paint composition, particularly a lacquer or a varnish and an aqueous coloidal dispersion of cerium

ABSTRACT

The invention relates to an aqueous paint composition, particularly a lacquer or a varnish and an aqueous colloidal dispersion of cerium. Said dispersion has a pH of at least 7 and comprises an organic acid with at least three acid functions of which the third pK is at most 10 or a salt of said acid with ammonia or an amine. Said composition has an improved water content and mechanical properties which improve throughout the life thereof or the duration of the presence thereof on the substrate for protection.

The present invention relates to a composition based on an aqueouspaint, in particular on a stain or on a varnish, and on a colloidalaqueous cerium dispersion.

Many substances are currently used in the furniture industry, joinery,the laying of floor boards and the building industry for protecting woodfrom damage due to light and bad weather in particular. It is known thatUV radiation, combined with water and oxygen, has the effect of rapidlytaking the color out of wood. Furthermore, when wood is used veryparticularly externally, it is also necessary to protect it from thegrowth of algae, fungi and various microorganisms.

Paints, and in particular stains and varnishes, are currently employedfor such wood protection.

However, the known stains and varnishes, which are complex formulationsbased on organic products, such as isocyanate complexes, for example, oninorganic products, such as iron oxides, or on protective additives,such as UV absorbers (benzotriazole, for example), exhibit a durabilityor a protective effect with regard to UV radiation which is not entirelysatisfactory. This is because organic UV absorbers can decompose overtime, they can migrate at the surface or they can be leached out by badweather. The known inorganic UV absorbers, such as titanium dioxides,have to be used in sufficiently high concentrations to be effective withregard to UV radiation but the increase in the concentrations occurs atthe expense of the transparency, of the resistance to water or of themechanical strength of the varnish or stain. Furthermore,UV-crosslinkable formulations are experiencing increasingly significantgrowth. In point of fact, organic UV absorbers can block thecrosslinking of the formulations when they are applied to wood.

Finally, for ecological reasons and reasons of simplicity of use, thereis an increasingly pressing demand for aqueous formulations, to whichthe solutions developed for organic formulations cannot be adapted.

There is therefore a need for aqueous paints and stains or varnishespossessing higher durability. This need exists not only in the woodindustry, as indicated above, but also in other fields, such ascosmetics, the protection of inks, of fibers or of fabrics, ofphoto-sensitive pigments or more generally of any volume situated behinda surface requiring protection from the harmful effects of UV radiation,of water and of oxygen or of one of these elements.

The object of the invention is thus to improve this durability.

With this aim, the composition of the invention is characterized in thatit comprises the mixture of an aqueous paint and of an aqueous colloidaldispersion of a cerium compound, this dispersion exhibiting a pH of atleast 7 and comprising an organic acid having at least three acidfunctional groups, the third pK of which is at most 10, or a salt ofthis acid, and aqueous ammonia or an amine.

The compositions of the invention which incorporate such a colloidaldispersion exhibit a resistance to water and a mechanical strength whichare improved, which thus increases their lifetime or the duration oftheir presence on the substrate which they protect. Their resistance toaging may also be increased.

Furthermore, in the case of the compositions based on emulsion alkydresins, the colloidal dispersion according to the invention has a dryingeffect, that is to say that it acts as crosslinking catalyst.

In addition, the presence of a colloidal dispersion according to theinvention makes it possible to retain the advantages described above,even in UV-crosslinkable compositions.

Other characteristics, details and advantages of the invention willbecome even more fully apparent on reading the description which willfollow and the various concrete but nonlimiting examples intended toillustrate it.

In the present description, the term “paint” is employed within thebroad sense to denote any coating of polymeric nature deposited on asubstrate which can have in particular a function of protecting thelatter and more particularly to denote aqueous paints proper, to denotevarnishes and to denote stains. The terms “stain” and “varnish” have theusual meanings in the technical field concerned here. It will bespecified, for the stain, that it is generally a transparent orsemitransparent formulation or composition applied to wood or to thesubstrate which is intended to protect it and which has a solids contentwhich can be of the order of 10% by weight or of the order of 40% to 50%by weight, depending on whether it is a base stain or a finishing stain.The varnish is a formulation or a composition which is more concentratedthan the stain.

Mention may thus be made, as paints to which the present inventionrelates, of paints based on the following emulsion resins: alkyd resins,the commonest of which is known as phthalic glycerol alkyd resin;modified resins comprising long or short oil; acrylic resins derivedfrom esters of acrylic acid (methyl or ethyl) and methacrylic acid,optionally copolymerized with ethyl, 2-ethylhexyl or butyl acrylate, andacrylic/isocyanate resins; vinyl resins, such as, for example,poly(vinyl acetate), poly(vinyl chloride), polyvinylbutyral,polyvinylformal, and copolymers of vinyl chloride and vinyl acetate orvinylidene chloride; aminoplast or phenolic resins, generally modified;polyester resins; polyurethane resins; epoxy resins; silicone resins; orcellulose or nitrocellulose resins.

The invention applies generally to any type of aqueous paint, inparticular to any type of stain or varnish, used on any substrate. Thissubstrate can in particular be wood or metals; in the latter case, forexample, the invention can be applied to automobile paints. Thesubstrate can also be a glass, of the type of glass used in constructionor glass intended to comprise photosensitive products or materials.Other possible substrates are protective coatings for organic orinorganic packaging, in particular when it is desired to retaintransparency in the visible light region. Mention may also be made, asother substrates, of fibers or fabrics. Thus, the invention can be usedin the protection of fibers or fabrics by coating these withcompositions comprising an organic binder or an emulsion resin of thetype described above and an aqueous cerium dispersion.

The invention also applies to varnishes used in cosmetics. Furthermore,the invention advantageously applies to UV-crosslinkable compositions,in particular to UV-crosslinkable stains, that is to say stains whichimmediately after their deposition on the substrate, in particular onwood, are subjected to treatment with ultraviolet radiation in order todry them.

Finally, it will be noted that the paint, stain and varnish compositionsobtained by the implementation of the invention respond to theecological restrictions due to the nonecotoxic nature of cerium oxide.

The expressions “aqueous colloidal dispersion of a cerium compound” or“aqueous cerium dispersion” or “cerium sol” denote any system composedof fine solid particles of a cerium compound, of colloidal dimensions,in suspension in an aqueous liquid phase. These particles can, inaddition, optionally comprise residual amounts of bonded or adsorbedions, such as, for example, nitrate, acetate or ammonium ions. The term“colloidal dimensions” is understood to mean dimensions of betweenapproximately 1 nm and approximately 500 nm. It will be noted that, insuch a dispersion, the cerium can be either entirely in the form ofcolloids or simultaneously in the form of ions and in the form ofcolloids.

The cerium is present in the dispersion generally in the form of ceriumoxide and/or of hydrated cerium oxide (hydroxide).

The particles of the cerium dispersion preferably have a size of at most200 nm, more particularly of at most 100 nm. This size can moreparticularly still be at most 10 nm. The sizes given here are determinedby photometric counting from an HRTEM (High Resolution TransmissionElectron Microscopy) analysis supplemented, if necessary, bycryomicroscopy.

The colloidal dispersions used in the context of the invention exhibitspecific characteristics. They comprise, first, a specific acid and,secondly, a base which is aqueous ammonia or an amine. Finally, theyexhibit a specific pH.

As indicated above, the acid is an organic acid, that is to say that itcomprises at least one chain of carbon atoms, it being understood thatit can, however, comprise heteroatoms. In addition, this acid mustcomprise at least three acid functional groups and its third pK is atmost 10. More particularly, this third pK can be at most 7.

The dispersion of the invention can comprise either an acid as definedabove or a salt of this acid. This salt can more particularly be analkaline salt.

In the dispersion of the invention, the acid interacts with the ceriumcation via any type of chemical bond. For this reason, the acid istherefore present on or within the particles of cerium compounds but itcan also be present in the aqueous phase.

Mention may very particularly be made, as suitable acid, of citric acid.

The level of acid in the dispersion, expressed by the moles ofacid/moles of cerium ratio, can be, for example, between 0.01approximately and 1.5 approximately, more particularly between 0.2 and0.5. It should be noted here that this level depends on the size of theparticles of the dispersion, this level decreasing as the size of theparticles increases. It will be noted here that the lower limit of thislevel is that below which the dispersion is no longer stable. The upperlimit depends in fact on the solubility of the acid used and also on themaximum amount of acid beyond which there is a risk of seeing thedispersion converted to a gel.

As indicated above, the dispersion also comprises a base which can beaqueous ammonia but also an amine. Any type of amine, primary, secondaryor tertiary, may be suitable. It will be noted that it is possible touse aminoalcohols, such as, for example, 2-amino-2-methyl-1-propanol.

The dispersions used in the context of the invention exhibit a pH of atleast 7 and which is preferably between 7.5 and 9.5, more particularlybetween 7.5 and 9. A pH of 7.5 at least makes it possible to havegreater effectiveness of the ingredients conventionally used in paints.

The dispersions which are suitable for the implementation of theinvention may be those disclosed in patent application WO 01/38225.

Dispersions usable in the context of the invention can also be preparedstarting from colloidal cerium dispersions to which an acid (for examplecitric acid) and a base (aqueous ammonia or amine), such as are definedabove, are added, so as to obtain the necessary pH value. The acid canbe added to the starting dispersion in a first step and then the base ina second step. However, it is possible to add the acid and the basesimultaneously. The starting colloidal dispersion may have beenobtained, for example, by the processes disclosed in European patentapplications EP 206 906, EP 208 581, EP 316 205, EP 700 870 and EP 700871. Use may very particularly be made of the colloidal dispersionsobtained by thermal hydrolysis of an aqueous solution of a cerium(IV)salt, such as a nitrate, in particular in acidic medium. Such a processis disclosed in European patent applications EP 239 477 or EP 208 580.In the latter application, for example, first of all a colloidaldispersion of a cerium(IV) compound is prepared by reacting an aqueoussolution of cerium(IV) salt with a base and then this dispersion istreated thermally, whereby a precipitate is obtained. This precipitatecan be resuspended in water and can thus give a colloidal dispersionwhich can be used in the present invention after addition of the acidand of the base, as indicated above.

The composition according to the invention can be prepared by simplemixing of the colloidal dispersion with the paint, in particular thestain or the varnish. The amount of colloidal dispersion used depends onthe final content of cerium oxide desired in the composition. Thiscontent can have any value. It may be noted that it is possible tooperate with high contents of cerium without, however, harming theresistance to water or the mechanical strength of the paint, stain orvarnish. Generally, a colloidal dispersion is used in an amount suchthat the cerium oxide content is at most 25% by weight, preferably atmost 10% by weight and more preferably still at most 3% by weight, withrespect to the whole composition. This amount is sufficient to make itpossible to have, at the same time, a paint, a stain or a varnish whichprovides effective protection of the substrate, in particular of wood,from UV radiation and which exhibits an enhanced durability.

Examples will now be given.

In these examples, the tests and the cerium sol described below areemployed.

Colorimetry

Measurement Conditions:

The calorimetric measurements are carried out according to standard ISO7724 using a Minolta CM 3610D spectro-colorimeter.

The measurement conditions are as follows:

-   -   specular included (all the backscattered intensity is measured),    -   the ultraviolet radiation is 100% filtered out,    -   the results are expressed under the illuminant/observer pair        C/10°.

The measurements were carried out on contrast cards, the paint beingapplied at 150 microns (paint in the wet state). In order to measure thetransparency, the measurements are carried out on the black backgroundof the contrast cards.

Resistance to Water

Measurement Conditions:

The resistance to water is evaluated by a measurement of contact anglebetween a drop of water and the paint or the stain using a Rame-Hartgoniometer. The higher the drop angle, the greater the hydrophobicity ofthe paint or stain and thus the lower the sensitivity to water. Thepaints or stains are applied to a contrast card; the paints or stainsare applied with a film drawer at a thickness of 150 microns.

Aging

The test is of the QUVA type. It is carried out under the followingconditions:

-   -   Irradiation conditions: UV-A lamp with a peak centered at 340        nm,    -   Chamber temperature: 60° C.,    -   Operating cycle: 4 hours of irradiation in the dry phase at a        temperature of 60° C. and then 4 hours of condensation in        darkness at a temperature of 60° C.

The moisture is introduced by heating a water tank situated at thebottom of the device (water vapor is thus produced) and then this watercondenses on the panels of paints.

Mechanical Strength

The mechanical strength of the stains is measured in two ways:

A hardness measurement is carried out on the stain film using the Persozhardness test. This test is carried out according to standard NFT 30-016(paints and varnishes—measurement of the hardness of a paint or varnishfilm using the Persoz pendulum). This test is carried out on varnishfilms applied at 150 μm or 300 μm (paint in the wet state) to glasssheets using an applicator of calibrated thickness. The characterizationprinciple is to measure the damping time of a pendulum resting, via twosteel balls, on the film to be studied. The hardness is expressed inseconds (time of one oscillation), which corresponds to the number ofoscillations of the pendulum when the latter is inclined by 12° withrespect to the normal at the start and 4°, which corresponds to the endof the test.

A measurement of scratch resistance is carried out using a Braivesclerometer. The sclerometer is a stylus equipped with a tungsten tip, apressure which can be varied using a calibrated spring being applied tothe stylus (the pressure is expressed in grams). The scratch resistanceis the maximum pressure (in grams) at which the tungsten tip of thestylus leaves no mark. This test is carried out on varnish films appliedat 150 μm (paint in the wet state) to glass sheets using an applicatorof calibrated thickness.

Test of Resistance to Methyl Ethyl Ketone (MEK)

The crosslinking throughout the body of the varnish films is tested byresistance to methyl ethyl ketone (rub test); a hydrophilic cotton swabimpregnated with solvent is applied to the paint and the number ofto-and-fro movements carried out before the paint is destroyed isrecorded.

Measurement Test on the Rate of Crosslinking of the Alkyd Binders byOxygen Consumption

The crosslinking reaction of the alkyd polymers is an oxidation reactionwith atmospheric oxygen. In the present case, the tests are applied at150 μm wet to aluminum sheets using an applicator of calibratedthickness. These sheets are subsequently introduced into a leaktighttest tube. After 24 hours, the variation in the % O₂/% N₂ ratio byvolume is measured by gas chromatography using a microGC M200microchromatograph from MTI. The ratio decreases because of the oxygenconsumption due to the crosslinking of the alkyd polymer. The dryingrate is expressed as percentage of variation in this ratio % O₂/% N₂with respect to the initial % O₂/% N₂ per hour and per m² of varnish.

Cerium Sol

In the examples which follow, the cerium sol used was prepared in thefollowing way. A CeO₂ precipitate, prepared according to example 1 ofpatent application EP 208 580, is dispersed in demineralized water, inorder to obtain a CeO₂ dispersion. The dispersion is left standing atambient temperature overnight (16 hours).

This dispersion exhibits a concentration of 103.7 g.l⁻¹ and its pH is1.35.

5.07 g of solid citric acid monohydrate, Prolabo Rectapur grade, areadded to 100 ml of this colloidal dispersion thus prepared, i.e. acitric acid monohydrate/CeO₂ ratio by weight of 0.49. The molar mass ofthe citric acid monohydrate used is 210.14 g.mol⁻¹ and the citricacid/Ce molar ratio is fixed equal to 0.40.

The system is homogenized for approximately 60 minutes. An amount ofaqueous ammonia, with a concentration equal to 10.8M, sufficient toobtain a pH of 8.7 is added to the latter system. The dispersionobtained exhibits a CeO₂ concentration of the order of 95 g.l⁻¹.

It is composed of monodisperse particles with a size of the order of 7-9nm.

For all the examples, the organic UV absorber is Tinuvin 1130 from Cibaand the inorganic UV absorber (titanium oxide) is Hombitec RM 400 fromSachtleben.

EXAMPLE 1

This example relates to a stain of conventional formulation of thestyrene/acrylic type, the formulation of which is described in table No.1 below: TABLE 1 Products Weight Description DS913 (Rhodia) 56.34styrene/acrylic latex Water 11.97 Monopropylene glycol 2.57 plasticizerProxel GXL (Zeneca) 0.10 biocide Tego 1488 (Goldschmidt) 0.20antifoaming agent Premix 1 Rhodaline RH5210 (Rhodia) 4.41 thickeningagent Rhodoline DP 1210 (Rhodia) 0.31 dispersing agent Tego 1488 0.20antifoaming agent Dowanol DPnB (Degussa) 4.11 coalescence agent Water4.23 Acematt OK 412 (Degussa) 2.40 silica Premix 2 Rhodoline RH5210(Rhodia) 1.46 thickening agent Troysol LAC (Troy) 0.40 anti-crateringagent Woodol 100 (Provigen) 2.04 fungicidal agent Water 9.28 Total 100solids content by weight: 28% pH = 7.2

The colloidal dispersion is incorporated by simple mixing at a contentof 1.4% of active material (cerium oxide) with respect to the total ofthe formulation. An organic UV absorber is incorporated in the same wayas above at a content of 1% with respect to the total to give acomparative formulation (2). An inorganic UV absorber is incorporated inthe same way as above at a content of 1.4% as dry matter with respect tothe total to give a comparative formulation (3).

The formulations thus prepared are applied to different substrates andare subjected to conditioning in the air in a controlled atmosphere (21°C.±2° C., 55%±5% relative humidity) for one week before theirevaluation. The results are given in table 2 below. TABLE 2 FormulationDescription 1, comparative Styrene/acrylic stain without UV absorber 2,comparative Stain with 1% organic UV absorber 3, comparative Stain with1.4% inorganic UV absorber 4, according to the invention Stain with 1.4%cerium (cerium oxide) sol

The results of the calorimetric measurements are given in table 3 below.TABLE 3 Black background Formulation L* a* b* 1, comparative 28.2 0.19−0.09 2, comparative 28.3 0.17 −0.03 3, comparative 34.9 −0.06 −7.07 4,according to the invention 28.6 0.02 −0.03

It is found, from table 3, that the color of the stains according to theinvention comprising a sol undergoes virtually no variation.

The results of the measurements of resistance to water are given in thefollowing table 4. TABLE 4 Formulation Contact angle (°) 1, comparative63 2, comparative 59 3, comparative 66 4, according to the invention 70

An improvement in the resistance to water for the stain according to theinvention comprising a sol, which thereby renders it hydrophobic, isrecorded.

The resistance to water is also evaluated by a measurement of change incolor (dE*) of the stain after contact with water. The tests areevaluated by colorimetry before and after the stain applied and a dropof water have been in contact for 15 minutes. The greater the colordifference, the greater the hydrophilicity of the stain and thus thegreater the sensitivity to water.

The stains are applied to contrast cards at a wet thickness of 150 μm;the calorimetric measurements are carried out on a black background.

The results are given in the following table 5. TABLE 5 Difference incolor after being Formulation in contact for 15 minutes 1, comparative7.6 2, comparative 9.4 3, comparative 17.7 4, according to the invention3.9

An improvement in the resistance to water for the stain according to theinvention comprising a cerium sol is recorded.

The mechanical strength results are summarized in table 6 below. TABLE 6Persoz hardness Formulation (seconds) 1, comparative 30 2, comparative30 3, comparative 31 4, according to the invention 50

The product 4 markedly improves the mechanical strength of the stain.

The aging results obtained from a test of the QUVA type are summarizedin table 7 below. The stains were applied to boards of maritime pineusing a brush, so as to have a weight per unit area of 325 g/m².

The difference in color (dE*) is recorded at two exposure times: 40cycles and 340 cycles. TABLE 7 dE* at 40 dE* at 340 Formulation exposurecycles exposure cycles 1, comparative 26 30 2, comparative 12 24 3,comparative 8 22 4, according to the invention 10 18

The times are expressed in cycles of 8 hours.

The product 4 markedly improves the resistance to aging of the paint.

EXAMPLE 2

This example relates to a stain of conventional industrial formulationfor external finishing of the dispersed acrylic/polyurethane type withthe commercial reference AZ930 originating from Arch Coatings France.

The colloidal dispersion is incorporated by simple mixing at a contentof 1.9% of active material (cerium oxide) with respect to the total ofthe formulation. An organic UV absorber is incorporated in the same wayas above at a content of 1% with respect to the total to give thecomparative formulation (6).

The formulations thus prepared are applied to different substrates andare subjected to conditioning in air for one week before theirevaluation. TABLE 8 Formulation Description 5, comparative AZ930 stainwithout UV absorber 6, comparative Stain with 1% organic UV absorber 7,according to the invention Stain with 1.9% cerium (cerium oxide) sol

The results of the measurements of resistance to water are given in thefollowing table 9. TABLE 9 Formulation Contact angle (°) 5, comparative69 6, comparative 69 7, according to the invention 81

An improvement in the resistance to water, indeed even a beading effect,for the stain according to the invention comprising a cerium sol, whichrenders the stain hydrophobic, is recorded.

The mechanical strength results are summarized in table 10 below. TABLE10 Persoz hardness Scratch resistance Formulation (seconds) (grams) 5,comparative 89 110 6, comparative 75 180 7, according to the invention146 260

The product 7 markedly improves the mechanical strength of the stain.

EXAMPLE 3

This example relates to a conventional decorative gloss paint based onacrylic latex with a pigment volume concentration of 16% and a solidscontent by weight of 49%.

The colloidal dispersion is incorporated by simple mixing at a contentof 1.5% of active material (cerium oxide) with respect to the total ofthe formulation. The formulations thus prepared are applied to differentsubstrates and are subjected to conditioning in the air in a controlledatmosphere (21° C.±2° C., 55%±5% relative humidity) for one week beforetheir evaluation. TABLE 11 Formulation Description 8, comparative Glosspaint based on acrylic latex without UV absorber 9, according to theinvention Paint with 1.5% cerium (cerium oxide) sol

The results of the measurements of resistance to water are given in thefollowing table 12. TABLE 12 Formulation Contact angle (°) 8,comparative 17 9, according to the invention 48

An improvement in the resistance to water for the paint according to theinvention comprising a cerium sol, which thereby renders it lesshydrophilic, is recorded.

The mechanical strength results are summarized in table 13 below. TABLE13 Persoz hardness Scratch resistance Formulation (seconds) (grams) 8,comparative 37 50 9, according to the invention 41 75

The product 9 improves the mechanical strength of the paint.

EXAMPLE 4

This example relates to a conventional decorative satin paint based onacrylic latex with a pigment volume concentration of 28% and a solidscontent by weight of 53%.

The colloidal dispersion is incorporated by simple mixing at a contentof 1.5% of active material (cerium oxide) with respect to the total ofthe formulation. The formulations thus prepared are applied to differentsubstrates and are subjected to conditioning in the air in a controlledatmosphere (21° C.±2° C., 55%±5% relative humidity) for one week beforetheir evaluation. TABLE 14 Formulation Description 10, comparative Satinpaint based on acrylic latex without UV absorber 11, according to theinvention Paint with 1.5% cerium (cerium oxide) sol

The results of the measurements of resistance to water are given in thefollowing table 15. TABLE 15 Formulation Contact angle (°) 10,comparative 59 11, according to the invention 67

An improvement in the resistance to water for the paint according to theinvention comprising a cerium sol, which thereby renders it lesshydrophilic, is recorded.

The mechanical strength results are summarized in table 16 below. TABLE16 Persoz hardness Scratch resistance Formulation (seconds) (grams) 10,comparative 55 75 11, according to the invention 60 125

The product 11 improves the mechanical strength of the paint.

EXAMPLE 5

This example relates to a conventional decorative matt breathing paintfor external application based on styrene/acrylic latex with a pigmentvolume concentration of 48% and a solids content by weight of 61%.

The colloidal dispersion is incorporated by simple mixing at a contentof 1.5% of active material (cerium oxide) with respect to the total ofthe formulation. The formulations thus prepared are applied to differentsubstrates and are subjected to conditioning in the air in a controlledatmosphere (21° C.±2° C., 55%±5% relative humidity) for one week beforetheir evaluation. TABLE 17 Formulation Description 12, comparativeExterior matt breathing paint based on styrene/acrylic latex without UVabsorber 13, according to the invention Paint with 1.5% cerium (ceriumoxide) sol

The results of the measurements of resistance to water are given in thefollowing table 18. TABLE 18 Formulation Contact angle (°) 12,comparative 79 13, according to the invention 90

An improvement in the resistance to water, indeed even a beading effect,for the paint according to the invention comprising a cerium sol, whichthereby renders it hydrophobic, is recorded.

The mechanical strength results are summarized in table 19 below. TABLE19 Persoz hardness Scratch resistance Formulation (seconds) (grams) 12,comparative 30 200 13, according to the invention 37 225

An improvement in the mechanical strength of the paint is recorded forthe product 13.

EXAMPLE 6

This example relates to a conventional decorative matt breathing paintfor interior application based on styrene/acrylic latex with a pigmentvolume concentration of 66% and a solids content by weight of 61%.

The colloidal dispersion is incorporated by simple mixing at a contentof 1.5% of active material (cerium oxide) with respect to the total ofthe formulation. The formulations thus prepared are applied to differentsubstrates and are subjected to conditioning in the air in a controlledatmosphere (21° C.±2° C., 55%±5% relative humidity) for one week beforetheir evaluation. TABLE 20 Formulation Description 14, comparativeInterior matt breathing paint based on styrene/acrylic latex without UVabsorber 15, according to the invention Paint with 1.5% cerium (ceriumoxide) sol

The results of the measurements of resistance to water are given in thefollowing table 21. TABLE 21 Formulation Contact angle (°) 14,comparative 93 15, according to the invention 103

An improvement in the resistance to water, indeed even a beading effect,for the paint according to the invention comprising a cerium sol, whichthereby renders it hydrophobic, is recorded.

The mechanical strength results are summarized in table 22 below. TABLE22 Persoz hardness Scratch resistance Formulation (seconds) (grams) 14,comparative 59 120 15, according to the invention 72 130

The product 15 improves the mechanical strength of the paint.

EXAMPLE 7

This example relates to an alkyd emulsion with the commercial nameUradil AZ554Z50 manufactured by DSM with a solids content by weight of50%.

The colloidal dispersion is incorporated by simple mixing at a contentof 0.35% of active material (cerium oxide) with respect to the total ofthe emulsion. The formulations thus prepared are applied to glass sheetsat a wet thickness of 300 μm using an applicator of calibrated thicknessand are subjected to conditioning in the air in a controlled atmosphere(21° C.±2° C.; 55%±5% relative humidity). TABLE 23 FormulationDescription 16, comparative Uradil AZ554Z50 emulsion without cerium sol17, according to the invention Emulsion with 0.35% cerium (cerium oxide)sol

The results of the Persoz hardness measurements, carried out afterdrying for 24 hours and 41 hours, are given in the following table 24.TABLE 24 Hardness at Hardness Formulation 24 hours at 41 hours 16,comparative 11 18 17, according to the invention 15 22

An improvement in the Persoz hardness is recorded, which implies thatthe cerium sol enhances the state of crosslinking of the alkyd polymerfilm.

The results of resistance to methyl ethyl ketone after drying for 41hours are summarized in table 25 below. TABLE 25 Formulation Resistanceto MEK (rub test) 16, comparative 2 17, according to the invention 6

The product 17 improves the resistance to methyl ethyl ketone, whichimplies that the state of crosslinking at the heart of the alkyd polymeris improved by the cerium sol.

The measurements of crosslinking reaction rates of the alkyd emulsion bymeasurements of oxygen consumption are summarized in table 26 below.TABLE 26 Reactivity of the drying Formulation (% variation % O₂/%N₂/h/m² stain) 16, comparative 23 17, according to the invention 38

The product 17 based on cerium sol accelerates the crosslinking of thealkyd polymer.

1-10. (canceled)
 11. A composition, comprising a mixture of an aqueouspaint and of an aqueous colloidal dispersion of a cerium compound, saiddispersion exhibiting a pH of at least 7 and comprising an organic acidhaving at least three acid functional groups, the third pK of which isat most 10, or a salt of this acid, and aqueous ammonia or an amine. 12.The composition as claimed in claim 11, wherein the paint is a stain, inparticular a UV-crosslinkable stain.
 13. The composition as claimed inclaim 11, wherein the paint is based on an emulsion resin of alkyd type.14. The composition as claimed in claim 11, wherein the pH of thecolloidal dispersion is between 7.5 and 9.5.
 15. The composition asclaimed in claim 11, having a ratio: moles of acid/moles of cerium, ofbetween 0.01 and 1.5.
 16. The composition as claimed in claim 11,wherein the acid is citric acid.
 17. The composition as claimed in claim11, wherein the composition has a cerium content, expressed as ceriumoxide, of at most 25%, optionally of at most 10%, by weight, withrespect to the whole of the composition.
 18. The composition as claimedin claim 11, wherein the colloidal dispersion has particles whose sizeis of at most 100 nm, optionally at most 10 nm.
 19. A process for thepreparation of a composition as claimed in claim 11, comprising thesteps of: a) mixing an aqueous paint with an aqueous colloidaldispersion of a cerium compound, said dispersion exhibiting a pH of atleast 7 and comprising an organic acid having at least three acidfunctional groups, the third pK of which is at most 10, or a salt ofthis acid, and aqueous ammonia or an amine.
 20. The process as claimedin claim 19, wherein the dispersion used in step a) is obtained byaddition, to an aqueous colloidal dispersion of a starting ceriumcompound, of the abovementioned acid and of the abovementioned baseuntil a pH of at least 7 is obtained.